There's not a lot of evidence that tips actually reliably vary in response to quality (easy to Google, but stuff like https://scholarship.sha.cornell.edu/cgi/vi

There's not a lot of evidence that tips actually reliably vary in response to quality (easy to Google, but stuff like https://scholarship.sha.cornell.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=1036&context=articles https://scholarship.sha.cornell.edu/cgi/viewcontent.cgi?refe... ). Tipping frequently matters more about the tippers mood, the tip-receiver's race and gender, and (of course) order size.